1. Field of the Invention
This invention relates to wind turbines and, more particularly, to wind turbine designs that maximize the frontal contact area of the turbine wings with the wind incident thereon.
2. Description of Related Art
The recent renewed interest in renewable energy sources has highlighted wind energy and the use of wind turbines to generate electrical power by harnessing the energy of wind currents. Indeed, many very large turbines have been installed or are being built around the world, typically employing towers 50 meters or more in height and turbine blades that may exceed 30 meters in length. These installations are successful in generating large amounts of electrical power, and because of their relatively slow rotational speed they tend to avoid negative impacts on local bird populations. However, it is apparent that the frontal contact area of the turbine blades of one of these typical turbines is a very small fraction of the virtual disk surface swept by the blades in a complete rotation, which leads to the conclusion that a great amount of wind energy is passing through the swept area of the turbine without contacting a blade or contributing any useful work toward power generation. Thus these turbines are necessarily low efficiency devices, when efficiency is calculated at a ratio of generated power to the wind power passing through the turbine's swept area.
In general, the long length of the blades tends to limit their width because of considerations of increased mass rotating, and increased lateral wind loads therefrom, at the top of the tower. Furthermore, the typical wind turbine blades rely on aerodynamic lift to generate rotational force, and the lift characteristic is often not directly related to blade width.
There are known in the prior art various attempts to devise windmills that employ flat blades to confront the flowing fluid transversely and receive the full force of the incident fluid, whether water or air. For example, U.S. Pat. No. 1,111,350 to Bayley describes a water current motor that has a central vertical shaft, and a pair of transverse pivot shafts extend through the central vertical shaft to support a pair of paddle-like blades, one at each end of each pivot shaft. The blades extend perpendicularly to their respective shafts, and the blades on each shaft are offset 90° each from the other about the axis of the pivot shaft. As one blade rotates into the wind it is urged thereby to rotate downwardly to a vertical position to catch the wind fully, while the blade at the other end of the shaft rotates into a feathered position. A cylindrical frame is secured about the central vertical shaft and is connected by rigid links thereto, and also connected to the outer ends of the pivot shafts for their support.
This device does not maximize the amount of power extracted from incident winds or fluid flows, and the torque it generates is not counterbalanced by any mechanical force other than the expedient of anchoring it to fixed points. Moreover, the pivot shafts extend diametrically through the central vertical shaft, and this factor prevents the use of a hollow tubular central shaft, a disadvantage that will be further explored in the following description of the present invention. In addition, the pivot shafts are supported at an upper quarter and medial portion of the central vertical shaft, causing the fluid force developed by the blades to be applied to the central and upper quarter portions of the vertical shaft. These forces are unbalanced and creates unbalanced intake and discharge flows.